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How are range and frequency related in HF communications?
How does the range of HF communications differ with frequency used? Is it less frequency more range, or more frequency less range?

I think HF is much more prone to be affected by atmospheric conditions which would then drive the choice of frequency. https://www.met.nps.edu/~psguest/EMEO_online/module3/module_3_2b.html#:~:text=HF%20users%20have%20found%20that,HF%20communications%2C%20but%20not%20always.&text=In%20these%20situations%2C%20it%20is,frequency%20higher%20than%20the%20FOT.

This is a very generic RF/physics question and is probably better asked on physics.se or ham.se. Have you tried searching those sites to see if your question has an answer there?

Neither or both, depending.
Unlike VHF and higher bands, which travel mostly via line of sight and therefore have limited range depending on altitude, HF radio relies on skywave propagation. This means the radio waves travel up, bounce off a layer in the upper atmosphere and then travel back down to the receiver. They may even bounce up and down between layers several times, allowing one to receive signals from the other side of the planet. You may be able to talk to stations far away but not nearby, or the bounces may not work the same in both directions. It’s unpredictable.
All of this odd bouncing depends on atmospheric conditions, which vary from place to place and even from hour to hour. Worse, different parts of the HF band will behave differently at the same time and place, so it has been broken up into several sub-bands of frequencies that tend to behave similarly.
That is why oceanic flights are given two HF frequencies in different sub-bands: at least one of them will probably work. Probably. And which one (if any) may change over the course of a long flight!
Worst of all, because of this long-range behavior, every station on the planet needs a unique frequency, and there isn’t a lot of bandwidth to go around, which is why it is chopped up into very narrow channels that give horrible sound quality. So, HF is only used when absolutely nothing else will work (or is available).

While I won't say weird is wrong -- because it is weird, a more helpful description would be unpredictable.

@Gerry Fair enough. Changed.

HF propagation over long distances depends on the ionosphere, and the state of the ionosphere depends on the sun — it varies with solar activity (which follows the 11-year sunspot cycle), time of year, and time of day.
The two most important layers of the ionosphere are the D-layer (60-90km above the Earth), which absorbs signals, and the F-layer (250-400km above the Earth), which refracts signals back towards the surface. (There's also an E-layer, which I will be ignoring for the moment).
D-layer absorption decreases with frequency, and increases with solar activity (and sometimes increases greatly when a solar flare releases a bunch of X-rays). During the day, and during periods of high solar activity, this absorption can make lower frequencies completely unusuable. At night, the D-layer rapidly fades away, and the lower frequencies "open up" (this is why you can sometimes hear distant AM stations only at night).
F-layer refraction also decreases with frequency and increases with solar activity. The way it works is that signals below a certain critical frequency will be refracted enough to come back down to Earth, but above that frequency they will fail to be refracted far enough, and continue off into space. When the solar activity is high, and the sun is high in the sky, the usable frequency climbs; when the sun sets, it goes back down, but the F-layer doesn't dissipate as quickly as the D-layer, so the result is more of a gentle drop over the course of the night.
F-layer refraction also depends on the angle at which the signal encounters the ionosphere — if the critical frequency is 5 MHz, then a signal going nearly straight up will come back down if it's below 5 MHz, and go into space if it's above 5 MHz. But a signal beamed near the horizon, grazing the F-layer at a much shallower angle and coming down thousands of kilometers away, can refracted even if its frequency is several times higher, say 15 MHz. This causes the curious effect that, when working above the critical frequency, you can talk to places that are far away, but not places that are nearby (unless they're so close that you can hit them with a line-of-sight signal, ignoring the ionosphere entirely).
Plus the ionosphere has its own "weather" conditions, and interacts with the Earth's magnetic field and the aurora in all kinds of interesting ways that would make this post even longer if I tried to explain them.
So in short, there's no straightforward relationship between frequency and distance, and the usable frequency (or frequencies) for a given path depend on the distance between the transmitter and the receiver, where the sun is in the sky in relation to both of them (time of year and time of day), the progression of the sunspot cycle, and a bunch of basically random factors that are difficult to forecast more than a few hours in advance.
As a visual aid, here is a map of (a prediction of) the highest usable frequency between a point in New Jersey and anywhere else in the world; the colors represent the different Amateur Radio frequency bands, which aren't relevant to aviation, but it should still convey the complexity:

What software did you use to make that nice graphic?

@rclocher3 it's from my own site, prop.kc2g.com. The code is open-source and the underlying graphical toolkit is matplotlib.

Very impressive!

It varies all over the place and depends on lots of stuff- here is a summary.
HF radio beams below about 30 megahertz that are aimed horizontally bounce back and forth between the earth and the ionosphere; so over-the-horizon propagation is common. If you are lucky you can bounce an intelligible signal all the way around the world on 100 watts and if you are really lucky you can do that with one watt or less.
Above 30 MHz the range of your signal becomes progressively more and more line-of-sight (i.e., it stops at the horizon), the beam no longer bounces off the ionosphere, and over-the-horizon coverage stops. In this regime, you get best range by putting your antenna on top of the tallest building or mountain possible, which geometrically puts the line-of-sight limit (i.e., the horizon) further away, thereby increasing the useable range.
Above 50 MHz your broadcasts are strictly line-of-sight and your radio signal starts getting bounced off of big buildings- so if there is a metal building blocking your line of sight, it will also block your radio transmission unless another metal building bounces some signal your way, around the other building. This regime is called multipath and is dominant at and above 100MHz.
Microwaves (300MHz to 300GHz) propagate more like beams of light than like radio waves, and are commonly focused into very narrow beams which have to be carefully aimed in order to hit the receiving antenna. They are also line-of-sight (although they can go through wood and plaster) and need the tallest towers possible to get the best range.

Though I would note that the degree to which microwaves are line-of-sight varies dramatically by frequency. Certainly, none of them are going to bounce off the ionosphere and reach a receiver halfway around Earth, but a 900 MHz, 2.4 GHz, or even 5.8 GHz Wi-Fi or cellular radio signal will go through normal interior walls without too much trouble and 900M/2.4G will work reasonably well even through normal exterior walls. The same cannot be said for a 30+ GHz signal.

@reirab, will edit.

HF radio waves, which have frequencies between 3 MHz and 30 MHz, propagate beyond line-of-sight by bouncing off the ionosphere.  The ionosphere is in the upper atmosphere, and it's made up of several layers of particles ionized by the sun.  One layer, which is called the D layer, scatters radio waves in all directions, which has the effect of absorbing radio waves.  The D layer only exists in daylight hours.  (You can't hear far-away AM radio stations in the daytime because the D layer scatters the radio waves.)  There are also the E and F layers, which bounce radio waves.  (To say that the waves "bounce" is an oversimplification; the waves actually refract.)  The E and F layers are strengthened by sunlight, and are weaker at night.
At any given time and place there is a maximum frequency, called the Maximum Usable Frequency (MUF), that radio waves will refract off the ionosphere.  Radio waves at frequencies higher than the MUF won't refract, but will instead radiate off into outer space.  Radio waves at frequencies just below the MUF tend to refract further than waves at lower frequencies.  The MUF changes quite a bit between nighttime and daytime.
The sun goes through an eleven-year solar cycle; at the peak of the cycle there are more sunspots and more ionizing radiation that energizes the ionosphere, and at the bottom of the cycle there are few or no sunspots and less ionizing radiation.  Where we are in the current solar cycle also has a large effect on the MUF.
Lightning produces a burst of noise across many frequencies, but especially at the lower HF frequencies (frequencies lower than about 10 MHz).  Lightning happens many times per second worldwide.  Radio noise from lightning propagates by refracting off the ionosphere just like manmade radio signals.  Noise from lightning makes use of the lower HF frequencies difficult when there are thunderstorms within radio range.  In my experience, use of the lower amateur HF bands (3.5 MHz, 7 MHz) is difficult in the US in the summer.
Because of the complex effects I mentioned, and others that I haven't such as solar storms, predicting HF radio wave propagation is a complex task.  Software to predict HF propagation exists, but I know from personal experience as an amateur radio operator that the software does a reasonably-good job of predicting average propagation, but real-world propagation changes varies quite a bit from day to day, and sometimes changes minute-by-minute, so actual conditions might vary quite a bit from predictions, for better or for worse.
Sorry for the rambling background, but as you can see, it's a very complex subject.  To answer your question, daytime HF propagation is more often better than nighttime propagation, but not always.  During both daytime and nighttime, higher frequencies tend to "skip" (refract) further, as long as the frequency is below the maximum usable frequency (MUF), but not always.  For someone who doesn't know much about HF propagation trying to contact another station on a short list of HF frequencies, I'd suggest to try the frequencies in order from highest to lowest.

I forgot to mention lightning noise in my answer, but yes, it's a very significant effect, especially in the tropical regions.

Yes but you remembered to include a graphic @hobbs ;)


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How does helicopter mustering make financial sense?
I've seen and know that helicopter mustering is popular in Australia and what I do not understand is why this works from a business perspective.
Helicopters are expensive and dangerous machines so it does not seem cost effective to round up cattle and livestock when it could be done, not as quickly, by people on the ground with ATVs and other wheeled vehicles. Not to mention the low-level flying is very demanding and tough on the machines and maintenance.
Surely it would be cheaper to employ extra people than pay the expensive hourly rate of a helicopter?

Speaking of "things you wouldn't expect would be profitable to do by helicopter but are", apparently helicopter-based cherry drying is a thing that exists.

I suspect it comes down to terrain and distances .. Some of the large stations in the northern parts of australia are really large (like 10-20,000 sqkm) - https://www.entegra.com.au/anna-creek-the-biggest-cattle-station-in-australia/. Also the videos I've seen often have a water component in them / water buffalo - and that's going to be hard work at ground level ..

@MrR I can confirm, having done aerial mustering, that without a plane it could take a whole day just to locate the livestock in a paddock. Undulating terrain, trees, gullies make it difficult to quickly travel the distance on the ground.

"Surely it would be cheaper to employ extra people than pay the expensive hourly rate of a helicopter?"  Either you're wrong, or they're wrong, and it's their money they're spending.  Ergo, either they have money to piss away, or there's something you're missing.

@RonJohn Yes, that's why they're asking a question here. I'm not sure what the point of your comment is.

@ChrisHayes I suspect that Ron's point was that the statement "Surely it would be cheaper..." should really be "Surely I must be missing something...".

Could someone bring some factual information about how much it costs per hour (or perhaps "per muster") for a bush helicopter + pilot ?

If using helicopters for mustering is surprising, you might also be interested in how they're used to harvest Christmas trees and dry fruit.

@user2705196 exactly.  "Surely it would be cheaper to employ extra people than pay the expensive hourly rate of a helicopter?" implicitly means that OP thinks that he knows more about the economics of helicopter usage than the people using the helicopters.

Two reasons:

It is way faster and allows one person with a relatively cheap-to-run R-22 to do the work of several cowboys.  You're paying for the cowboy 24-7 if they are on staff, which is usually the case on a sprawling and remote ranch/station where you have to keep them on full time (and the horse if using them); you're only paying for the machine (direct hourly operating costs at least) while it's running.
It almost eliminates losses from stragglers that get missed and later become dinner for predators.  This feature was a welcome surprise when gyrocopters and helicopters were first tried out. Originally, gyrocopters were used to help out with the cowboys, mainly to hunt for strays that couldn't be seen from ground level. When the R22 came out, being able to hover and maneuver in confined areas, it became feasible to do both the mustering and overwatch role from the air.

Between the two, the business case starts to favour the helicopter.  If it didn't, they wouldn't do it. Granted, it is pretty dangerous flying, not for the faint of heart, but there are lots of young pilots keen for a thrill.

Your note about "paying for the cowboy 24-7" might not necessarily be clear if someone isn't familiar with exactly how isolated (and enormous) Aussie cattle stations can be. Perhaps add a bit more context to that?

@SebastianLenartowicz - Actually, it would be similar regardless of the area. Even in the US, the majority of cattle hands are either permanent, seasonal, temporary, or as needed. Very few will be paid hourly. This is a job without a punch clock. Maybe a time sheet can be used for part-timers and as-needed personnel. But, the hours can be so long and varied, that it would not make sense to pay per hour. On the other hand, an R-22 can be operated for $100-200 an hour, not including the pilot.

I recall when reading about Aussie helicopter mustering years ago that the savings from the reduction in losses from overlooked strays was surprisingly high and is really what clinched the business case.

Personally, I don't see how it's financially viable in most situations, but I'm guessing it's financially viable in a few situations or when shorthanded.
Although horses are expensive to "maintain", almost every ranch already has them.  Feed and medical are the two largest expenses, and you're going to be providing that whether or not you are using them for mustering/herding.  Horses fart and breathe, but besides that, they don't produce exhaust.  I'm guessing they produce methane, but I've never measured it myself.  They also produce manure that enriches the soil.  Their hooves help break up the soil, which allows grasses and plants to prosper.  Animals like horses, bison, and cattle are good the health of the land.
ATVs are inexpensive to fuel and somewhat inexpensive to maintain; they are not too expensive to purchase.  ATVs produce toxic exhaust.  Unlike horses, they compact the soil, which inhibits grasses and plants from growing.  Over time, ATVs can be bad for the land, but using them on the same tracks can significantly help reduce this degradation.
Helicopters are expensive to purchase (or rent) and time-consuming to properly maintain.  Fuel and maintenance costs will depend on the model.  Helicopters produce toxic exhaust.  Helicopters can cause loose soil to get moved, but this is usually not a problem, as the net effect is usually minimal.
There are two situation where I can see a helicopter being an advantage over horses and ATVs:

When you are shorthanded.  As the size the of the herd increases, and the size of the range increases, you need more cowgirls and cowbows on horses or ATVs to manage the task.  A helicopter could help in shorthanded situations.

When the range exceeds that which horses or ATVs can travel while having the feed/water or fuel they need.  For horses, this depends entirely on the breed, condition, and age of the horses and the breed, condition, and age of the herd.  If appropriate and sufficient food/water will not be available for the horses, but will be available for the herd, horses may not be viable.  I have never seen this happen, but I could create a contrived example to make it happen, and it's possible such real-world examples exist.  For ATVs, I think it's more obvious.

Meaning absolutely no disrespect to John K whatsoever, I will politely disagree with two of the reasons he posted:

Speed.  The limiting factor of moving a herd is typically the speed of the herd itself.  A helicopter does not move a herd faster (unless you are doing something inappropriate with the helicopter and causing the animals undue stress).

Stragglers.  Skilled ranchers don't leave stragglers.  Yes, mistakes can happen (such as an animal stuck in the brush and not being seen), but they are very rare, and a helicopter could make the same mistake.  Since a helicopter pilot cannot hear an animal crying, a calf calling its cow, or its cow responding,  I think the risk of stragglers would actually be greater with a helicopter.  It's possible a helicopter provides some sort of advantage here that I'm not thinking of, but I have never flown a helicopter for this purpose, so I am not personally aware of any.  A helicopter could sweep a large area after moving a herd, but I've always used fixed-wing aircraft for periodic sweeps of large areas, not a helicopter.

John did mention cost, and I wonder if this is a primary factor.  Cost will depend on many factors and variables, so we don't have a clear picture.  I can create theoretical situations where employing helicopters would be cost-efficient, and those in which they would not be.  But since there are at least a dozen different variables at play, it would really depend on the exact situation.

A lot is going to depend on terrain.  In open & fairly flat country, I can see how a helicopter might be useful.  Around here, where a lot of the open range grazing is small meadows interspersed with forested mountains, probably not useful at all.

@jamesqf Yes, definitely.  In some terrain a helicopter would likely only represent a liability.  That said, I watched, with a little disbelief, this guy who trims massive trees using a crazy rig with huge swirling sawblades attached to his helicopter via a shaft.  Skilled genius, or a disaster waiting to happen... you decide!  (And history will eventually reveal.)

@RockPaperLz-MaskitorCasket Those are awesome! https://en.wikipedia.org/wiki/Aerial_saw One was used by the villains in a James Bond movie in the 1990s, IIRC.

@ceejayoz Yes, that is them!  Good find!  Now that you mention James Bond, I also have a faint recollection of one being used in one of those films or books... (3 minutes elapse...) I found it... The World is Not Enough (1999).  I don't know if the aerial saw they used in that movie was an industrial one, or a creation of their prop team (or even full/partial SFX), but that's the general crazy idea!  Here's a link to a clip from that movie featuring the aerial saw: https://www.youtube.com/watch?v=3aL1VF9zlfM

Hmm, a lot of the statements up top of this answer could be just wrong.  For example, i's really, really REALLY expensive to keep a string of horses, it's a deep infrastructure problem.  (A random example, it would be trivial to spend 100 grand a year merely on the incidental issue of pickup trucks and trailers to haul the horses around 100s of km.  Hence, "almost every ranch already has them" this is just wrong.  Horses are an incredibly expensive novelty, and the one and only reason to have them is for muster.

Something that strikes me as odd is your statement about toxic exhaust. Turbine helicopters would be expensive to own and operate. Most of the aircraft herding operations that I know of or have seen use piston aircraft. In which case, except for a slightly higher lead count, they will have a very similar carbon footprint to a couple of ATVs or one truck. Even turbine helicopters burn the equivalent of clean diesel. An R-22 can efficiently operate at less than a 10 GPH at 100 MPH fuel burn rate. A truck will operate at 10MPG at 100 MPH. Normal ATVs can not reach 100 MPH.

I met a guy at the last US Helicopter Safety Alliance Safety Stand-Down who owned a business that did helicopter underslung operations like rotary-saw tree trimming. In most s was done in areas that had to be trimmed for power lines on a regular bases in very hard to reach areas. There is always a cost-benefit analysis to these sorts of things to justify the risk and expense. Otherwise, it would not be done.

@Fattie: I have to disagree about horses being "an incredibly expensive novelty", 'cause I've been supporting a couple for the last decade or more.  They're not all that expensive, especially if you have adequate grazing.  You do have a point about the expense of hauling them long distances, but that depends on the area you're grazing.

hi @jamesqf for sure, I'm talking in the context of the question.   (to wit, the handful of ridiculously massive ranches on Earth, that (amazingly) use choppers for herding since (again, amazingly) it's cheaper.)  to operate the battalion of horses + cowboys needed for that (once a year project) is a huge operation at the scale of "buildings, entire staffs, etc".  Indeed!!!!  note that ranches of this scale that do use cowboys + horses to herd, of course just hire a specialized crew of cowboys + horses at that time of year

@Fattie: But those amazingly huge ranches are the exception, not the rule.  More reasonably-sized ranches do have the horses, and use them, especially in difficult terrain.

@jamesqf - yes - absolutely !  As I understand it, the question is about the 5 ranches in the far north of Australia, etc, where (amazingly) they use choppers.  Horses are the best !

@Fattie wrote "i's [sic] really, really REALLY expensive to keep a string of horses" and "Horses are an incredibly expensive novelty, and the one and only reason to have them is for muster". Those are odd things to say, as they are all incorrect.  Horses have dozens of uses on a ranch as well as many uses on a farm.  On most ranches, they are a requirement, not a luxury.  Ever try roping cattle from a helicopter?  How about moving massive bulls with a little ATV?  Good luck partner, and I hope you have a good hospital nearby!

@DeanF. wrote "Something that strikes me as odd is your statement about toxic exhaust."  I was simply being comprehensive, and those were just a few words in a long answer.  It's all about tradeoffs, values, and pride.  Some ranches pride themselves in not using any combustion engines for labor, but most do.  Regardless, it's important to be aware of the impact of our decisions when we choose to use devices that emit toxins and be aware of alternative that do not.  That said, sometimes the alternatives have their downsides, which is why I mentioned that horses likely produce methane.

@DeanF. wrote "An R-22 can efficiently operate at less than a 10 GPH at 100 MPH fuel burn rate. A truck will operate at 10MPG at 100 MPH. Normal ATVs can not reach 100 MPH."  If you're trying to drive a herd at 100MPH, you're doing it wrong.  Either that, or you are are herding unusually fast coalitions of long-range cheetahs. ;)

@RockPaperLz-MaskitorCasket - You do realize how popular fast food is here in the US. Don’t you? . My point was that fuel consumption and carbon footprint were similar. I used a convenient universal measurement for comparison.

@RockPaperLz- Mask it or Casket: You don't use the 100 mph of your helicopter, or FTM whatever top speed your truck, ATV, or horse can manage, to drive the cattle in a straight line.  You use it to circle outside & behind the herd to keep it moving in the direction you want.  You really don't want the cattle moving at more than walking speed, as they lose weight from the exercise.

@jamesqf Yes, that is what I was saying.

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Why hasn’t SpiceJet painted their own logo on their newly acquired aircraft?
So I’m referring to the airline company SpiceJet here. They have acquired old airplanes of the company that has now gone under, Jet Airways.
The above plane is clearly an old Jet-Lite plane that SpiceJet acquired, my question is why don’t they paint the fin or even the body with SpiceJet colors and logo?
Is it not economical or just not worth anything to the company to do so?

Painting an aircraft is expensive, not just materials and labor but downtime. Low cost carriers operate on very low margins, they may not have the budget until it's down for other reasons like a check.

Also, given that the photo is from FlightRadar24 - a private company, not a government or licencing body - there is no guarantee that the photo is up-to-date.

Well, I also saw the plane directly overhead and it wasn’t painted. Haha.

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What are those green LED arrays on top of the instrument panel called?
Below is the link showing a fire fighting aircraft

From 0:23 to 0:45 an LED array can be seen. The peculiar thing about that is as aircraft approaches the site, all the LEDs are glowing, and vice versa when the aircraft leaves the site.

The lights are for the tanker drop system. The individual lights indicate tank door status. Green means armed and ready to drop. This video shows the same type of aircraft doing a partial load drop with 4 tanks remaining full after the drop. https://youtu.be/oSC5PriYrI4

The aircraft is an Avro RJ. I don’t see all the lights “glowing” as they depart. When they drop at 0:37 you can see all the lights flashing and then only they go out with a single green flashing on the right. (probably one door closing a little slow). As they climb away you see one solid green visible on the left side which is probably the system master light.

Thank you Gentleman.


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When should the fuel pump be on in a Cessna 152?
I am a new student and just need help understanding the fuel pump system. For a Cessna 152, in which scenario would I have the fuel pump on ?
Start ?
After Start ?
Before Take-Off ?
After Take-Off ?
Changing tank selection ?
Stalls/Spins ?
Approach and Landing ?
After Landing ?

I've never seen a 152 with a manually operated fuel pump, it's a gravity fed system with an enginne driven pump - you dont switch it on or off as such

related (or duplicate if you remove the 152 detail): https://aviation.stackexchange.com/questions/21993/when-is-a-fuel-pump-needed-on-ga-aircraft


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What are the approach speeds for each flap setting in a Cessna 152?
I am still trying to understand how the approach speeds for different flap speeds work. I cant find it in the handbook but I want to know the different approach speeds for the following flap settings:

0 degree Flap
10/15 degree Flap
20/25 degree Flap
39/40 degree Flap

Do you mean the maximum speeds for flaps? Or do you mean stall speeds? As Jamiec said, flaps don't change your approach speed, but there is a maximum speed at which you can deploy flaps...

@757toga some folks may be looking at it another way:  an assigned approach speed and glide angle (like 3 degrees).  In that case (for example a commercial aircraft), flaps (and power) would be determined by weight for a given airspeed and AOA.

FLAPS 0 can used for a higher approach speed when
there is wind.  This "clean" configuration will give you the greatest gliding distance (least drag per distance flown).  Approach speeds are higher and the glide angle is flatter.  This is fine when one has adequate runway to work with.  With 0 flaps, the wing has less camber and lower coefficient of lift.  It makes up for this by going a bit faster.
Flaps 10 is used for short field approaches.  It increases wing camber and coefficient of lift, allowing the aircraft to approach around at a slower speed while still generating adequate lift.  Because there is greater drag, the glide angle will be slightly steeper.  Better to use this one if the landing area is shorter.
FLAPS 20, 30 (and 40) serve to further steeper the glide angle by increasing drag.  These flap settings generally do not increase lift much more and are not used for that purpose because they are excessively draggy.
FLAPS 10 can also be used for short, soft field takeoffs, but the plane climbs more efficiently at Vy, with FLAPS 0.
More reading about flaps here.
Another way of looking at it is:  increasing coefficient of lift by increasing camber allows one to fly at the same Angle of Attack at a lower airspeed.
Angle of Attack and Camber form the Lift Coefficient.  Too great and angle of attack causes a stall, so it is smarter to increase camber to fly more safely at a lower airspeed.
The variables of lift related to aircraft configuration and velocity are explained in the Lift Equation:
Lift = Density × Area × Lift Coefficient × Velocity$^2$.
Note that velocity is squared.


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How to interpret the electrical information on a G1000 T206H?
I have a T206H and The POH says:

Current indication (AMPS) for both the main and standby batteries is
  provided at the bottom of the EIS bar (along the left margin of the
  MFD or PFD), labeled M BATT S. Main battery current is numerically
  displayed below the M. Main battery current greater than -1.5 amps is
  shown in white. Standby battery current is displayed numerically below
  the S. A positive current value (shown in white) indicates that the
  battery is charging. A negative current value (shown in amber)
  indicates that the battery is discharging. In the event the alternator
  is not functioning or the electrical load exceeds the output of the
  alternator, the main battery ammeter indicates the main battery
  discharge rate.

The part that confuses me is the one that says:

Main battery current greater than -1.5 amps is shown in white.

Does that means that when the number is negative but greater than -1.5 it is OK, because it is in white?
And after 40 minutes of flight in normal daytime operations I have a -1.0 in the M BATT amps but the M BUS volts remain 28.3. What does this mean?

You've actually answered your own question back there:

A negative current value (shown in amber) indicates that the battery is discharging. In the event the alternator is not functioning or the electrical load exceeds the output of the alternator, the main battery ammeter indicates the main battery discharge rate

The 28.3 Volts reading is the electric energy charge supplied by the aircraft alternator (60-Amp alternator is standard and a 95-amp one is optional) through the main bus, whereas the M amp reading is what's happening to the main battery. In the situation you've described, you've got so many electrically-powered systems running, that the alternator, though operating normally, is unable to supply them all, so additional power is drawn from the battery.
The 206 PIM states that the Main battery Ammeter is color-coded white for values greater than -1.5 Amps, meaning that Cessna is not concerned with battery drains of 1.5 Amps or less (i.e. readings between -1.5 and 0). If the discharge rate is greater than 1.5 Amps (reading lower than -1.5), then the reading will be color-coded yellow. See below for an example of this.

Ok. I understand that the reading of the ammeter between 0 and -1.5 is considered by cessna of no concer if i am using much more load than The alternator output.   But the thing is that I was not. It was day time, no light on but the bacon, no AP, dead-reckoning flight, and still -1.

Ok. I understand that the reading of the ammeter between 0 and -1.5 is considered by cessna of no concer if i am using much more load than The alternator output.   But the thing is that I was not. It was day time, no light on but the bacon, no AP, dead-reckoning flight, and still -1.0 on the M Batt Amps.    I have checked the lamar MCU, I try a new battery, I checked the alternator but still -1.0.   What else do you suggest?

@MarkDavidMaduroGuerra - that sounds like a tricky one; from what you've described, the alternator should be more than capable of handling the load, but, for whatever reason, the battery was still discharging. For electrical gremlins like that, I'd take her to an A&P for a look. Things that might cause something like to happen could include an alternator that's no longer up to scratch, a battery that might not be adequately isolated and is finding a pathway to drain to somewhere, maybe even a faulty sensor or software glitch giving erroneous readings in the cockpit.

Thanks habu. I will take Her to a Cessna servises center. This is draving me crazy. I am suspecting the amperage sensor. I will conecte a hand tester to compare its  reading and the PFD ammeter reading.

@MarkDavidMaduroGuerra - good luck, and, when you find out, come back here and let us know what it was.

Hi. I solved The problem. I Had To take Her To The cessna services Center and they performed a calibration steps om the G1000. They get into the comfiguration mode of The g

GEA 71 and checked first if The GEA was properly working and then after that they proced With The calibration steps acording To The last line mantenance manual for G1000 Nav iii cessna.

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text:
How do pilots know when they have to start the descent?
I am trying to understand how pilots do know when to start descending, I have read that mostly it is from the FMS information and ATC clearances (Aviationvector.com). And on some other references, they mention it is up to the pilot (USA today).
Which one is true? Or are they both true?

Are you specifically interested in airliners, or just in general? ie, I don't have a FMS in my cessna, and I'm often not under control of ATC, but I still know when to decend!

The vertical navigation part of the FMS, if it has it, will compute and display an ideal TOD (top of descent), but in the end that's more or less a "suggestion" in controlled airspace, and you can only follow it if you cleared to descend by ATC (unless you declare an emergency).
The center controller knows when to start you down, and will normally issue a descent clearance before you get to TOD, either to descend as soon as instructed for separation purposes, or at your discretion. If at your discretion, you are then free to follow the Vnav guidance.
If you don't have a Vnav feature in your FMS, and you are free to descend at your discretion, the rule of thumb is 1000 ft in 3 miles. So if you're descending from FL310 to 10000 ft, you start down 63 miles (21 x 3) from the point at which you need to be at 10000 ft (add some distance if there is a significant tailwind, and vice versa if there is a headwind).

Its pretty easy to use some approximate calculations.
If I'm at 10,500 feet, and I need to descend to 2,500 feet for TPA,
then its pretty obvious I need to drop 8,000 feet.
My typical descent rate is 500 ft/min, so it is going to take me 16 min to make that descent.If I'm planning a faster descent of 1000 ft/min, it will take me 8 minutes.
My airspeed is around 100kts, or about 1.6Nm per minute.
So, in the 16 minutes of descent, I'll be covering roughly 25NM.
(neglecting the difference between slant-distance and ground-distance... this is all approximations for planning purposes)
When my map or my DME indicates I'm 25NM away, and my clock shows I'm about 20 minutes from destination, I'll start a standard 500ft/min descent, and I'll be pretty close to TPA as I get closer.   Of course, I can revise and adjust as needed, if I'm descending slower than planned, or IAS is faster than planned, etc.
This should both be part of your pre-flight planning, and also something good to do if you're bored during the cruise portion of flight.

$$ \text{Descent Height} = \text{Cruise Alt} - \text{TPA}$$
$$ 8,000ft = 10,500ft - 2,500ft $$

$$ \text{Descent Time} = \frac{\text{Descent Height}}{\text{Descent Rate}} $$
$$16 \text{min} = \frac{8,000ft}{500 fpm}$$

$$ \text{Start Descent DME} = \text{Descent Time} \cdot \frac{IAS}{60} $$
$$ 26.6NM = 16 \text{min} \cdot \frac{100 \text{Kts}}{60 \text{min}} $$

With a small GA aircraft like a Cessna that is not flying terribly high nor fast, approximations and round figures are totally fine.
Larger or higher performance plans need more precision. In a descent from FL020 at 180Kts, there is less margin for error to make a safe and efficient descent. That is where an FMS, ATC Control and Procedures are more important.
But the general approach is the same. It is still a basic math problem of Distance, Rate & Time to begin a descent at a specific distance and time to reach a specific target.

This is much better than the answer I was about to write from a light aircraft approximation POV.

Isn't it easier to use angle of descent rather than rate? Because the true airspeed and rate of descent both increase with altitude, but the angle you get with engine at idle stays roughly constant, no?

@JanHudec I do not see how.  You should provide an example.

Instead of targeting 500 ft/min, if you know you descend 1,000 ft in 2.5 NM with closed throttle you just use that (8,000 ft × 2.5 NM = 20 NM), then close the throttle and maintain speed with pitch (the flight level change A/P mode does exactly that). Or decide you want to descend 1,000 ft in 3 NM (the usual value) and adjust the residual power according to whether you are descending slower or faster than that (while still maintaining speed with pitch).

Interesting idea, but I do not know the descent-vs.-distance numbers for my plane. (maybe I should?)   But the 500fpm descent is clearly marked on my VSI right in front of me.

@JanHudec I was taught 3 miles per 1000ft in a C172.  But when I moved up to faster planes, that gave an uncomfortably high rate of descent, plus it didn’t account for winds aloft, so now I use a “pilot math” simplified version of this answer’s general method.

It could be one, or the other, or both. This is largely dependent upon what operational rules you are using, what air space you were in, and what the requirements of ATC are.
For a VFR flight in Class G airspace, it’s all up to you.  You are PIC; it’s up to you to your discretion to descend.  This also applies to VFR flights in Class E airspace as well, with or without flight following.  If you are using flight following, a controller may ask you to start a descent to accommodate traffic congestion or other airspace rules in the terminal area.
Making the descent into a terminal area for landing on your own can be done a number of ways.  I have often done this in the following manner:  First, decide on the altitude you want to lose prior to arrival at a waypoint, the rate of descent you want to use and the ground speed you want to maintain throughout the descent.  Next divide the altitude to lose by desired rate of descent.  This gives the time you will spend in descent in minutes.  Multiply this figure by the ground speed and divide by 60.  This gives the distance out from the airport or waypoint which you must begin your descent.  EXAMPLE:  You’re cruising at 12,500 ft MSL preparing to descend and land at an airport with a field elevation of 3,200 ft.  You are currently cruising with a ground speed of 200 knots.  It’s s VFR flight, so you intend to arrive at traffic pattern altitude of 1000 ft AGL, or 4,200 ft MSL.  This requires you to lose 12,500-4,200 ft = 8,300 ft.  You desire a gentle descent of 500 fpm, therefore the descent will take 8,300/500= 16.6 min or 16 min, 36 sec to complete.  Therefore you must start your descent at 16.6(mins)*200(nm/h)/60(mins/h) = 55.3 nm from the airport.
At lower altitudes, and if you have a visual waypoint or airport inside sight, you can pitch down gently then trim the airplane up so the waypoint rests right on top of the nose or cowling.  This is a good one for arriving into a VFR traffic pattern at altitude.
Modern flight management systems have vertical navigation planning, where the pilot simply enters what altitude they want to be at, at a certain way point, or distance from a waypoint, and the system can automatically compute a time of descent point to begin their descent at.
In IFR, these decisions are often made for you by ATC, as they will tell you what altitude, or block of altitude they want you at. Often times, on more congested routes, ATC may give you a clearance such as “climb via CWARD2 Departure or “descend via POWDR2 arrival”.  In this situation, ATC expects you to follow the pre-planned altitude and descent schedules listed on the SIDs or STARs.  Here you will have to use your own judgment to make sure you arrive at the altitude and or speed restriction listed for the fixes.  Another common ATC clearance is “descend at your discretion, cross DOBOR at FL240”, where are you were expected to descend however you like, but make sure you cross the DOBOR fix at FL240.

It's not nice to start a dissent with ATC whether you're using flight following or not! :D A descent, though, is a different matter. ;)

They are both correct in their own way.
The conduct of the flight is pilot’s responsibility so in general they determine when to leave cruising altitude.
Modern aircraft FMS calculates the top-of-descent point (TOD) which is more or less accurate depending on the software and the actual conditions. For example, most sophisticated systems take into account winds, weight of the aircraft, any airspace restrictions, some kind of temperature model and even the optimization between flight time and fuel cost to produce optimal descent profile while some simpler systems might approximate the descent with some fixed angle, usually somewhere around three degrees. On top of that pilots have developed some kind rules of thumb to estimate required distance to descent which are then augmented by sophisticated guesses based on their experience.
On the other hand, especially in busier airspaces all that is theoretical. Sometimes air traffic controllers take very active role in descent planning as they are trying to push maximum amount of traffic through their airspace, leaving the pilots cursing in cockpits when they are forced to deviate from their optimum and/or comfortable flight profiles :)


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How is Fuel needed to be consumed calculated when MTOM and Actual Mass is known
I'm practicing for my EASA PPL(A) exams and one of the questions I came across looks like this:

How much taxi fuel must be consumed before take-off to reduce the
aircraft mass to the maximum take-off mass?
Maximum ramp mass (MRM): 1150 kg Actual ramp mass: 1148 kg
Maximum take-off mass (MTOM): 1145 kg (1,00 P.)
Possible answers:

2L
3L
5L
4L

Now, my thinking was Fuel needed to be consumed = Actual ramp mass - MTOM => 3L
But it seems the correct answer is 4L. I don't understand why.

This looks like an ATPL question. Is this really on the EASA private pilot exam?

Your thinking is correct, the fuel needed to be consumed is indeed the actual ramp mass - MTOM. That results in 3 kg of fuel.
What you forgot is to convert the weight into a volume (note that the answers use litres). According to Wikipedia Avgas has a density of 0.72 kg/L, so the answer is:
$$ \frac{1148 \, \text{kg} - 1145 \, \text{kg}}{0.72 \, \text{kg/L}} \approx 4.17 \, \text{L} \approx 4 \, \text{L} $$

It is a good question! Converting between volume and weight is extremely important to get right in aviation. One example that comes to mind is the "Gimli Glider" accident (see wikipedia or youtube).

(Very much non-pilot here) If the exact answer is slightly above 4, and the only answer alternatives given are 2, 3, 4, and 5, shouldn’t the correct answer be 5, since burning 4 liters still leaves you 0.17*0.72 ≈ 0.12 kg overweight? Admittedly, 0.12 kg is probably within the measurement error, but I would expect that one would want any rounding to go in a "safe" direction.


text:
What is the reason the MDA for VOR approaches differs from the DA for ILS approaches?
What is the reason for the numerical difference between the MDA altitude in VOR approaches and the DA altitude in ILS approaches?

Related: What is the difference between ILS and VOR/DME?

The simplest answer is that non-precision approaches (e.g. LOC or VOR) nearly always have higher minima than precision approaches (e.g. ILS).
Precision approaches provide strict vertical guidance: the pilot flies a constant descent angle down a precise glide slope/path, and if they don’t see the runway by the time they reach the DA, they immediately climb and execute the Missed Approach Procedure.
In contrast, for a non-precision approach, the pilot descends at various step-down fixes until the MDA, and then flies level (aka “dive and drive”) until they either see the runway or reach the MAP. Allowing an IFR aircraft to be flying down low for a longer period of time necessarily requires a much larger, flatter OCS.
The entire OCS must be raised to a certain height above any obstacle or terrain within its lateral boundaries, so a large OCS will naturally be higher than a small OCS. For instance, a radio tower or tall building three miles from the runway may be within the large, flat OCS for a VOR approach, forcing a high MDA, but not the small, tilted OCS for an ILS approach, allowing a low DA.
There are rare IAPs with an MDA lower than the DA, but they usually require a step-down fix with a very high descent angle after a close-in obstacle. IAP designers avoid this, however, unless there’s no other way to create a procedure with at least one decent minimums line.

Out of curiosity: could you add an example for an approach with a lower MDA than DA?


text:
Continuing Airworthiness Requirements During Major Modification
I am involved in a program where the aircraft (B737) will undergo a major modification taking approximately 2 years which will ultimately result in a new type certificate being issued under a new authority. (Foreign)
My question is do you continue with the continuing airworthiness requirements of the current document set i.e. MPD and other such manuals published as part of the current type certificate (A16WE) issued by the FAA until such time that the modification is released and new type certificate issued or does the design organization embodying the modification take control of all continuing airworthiness documentation and decide what happens and when?
My thinking is, irrespective of the aircraft eventually becoming a new type it has history and it has a current type certificate therefore my expectation would be you should continue to manage the current continuing airworthiness requirements associated with its current type certificate requirements. Only once the modification is completed does the new document set become applicable because only then would the new type certificate come into effect.

In case it is relevant: could you add in which country the modification is done or at which authority the new type certification will be applied for?

I would expect it depends on what is being modified. The expectation would be that parts not being modified and subject to CAR would have to be compliant with CAR under the new TC - through either routine action or a catchup action prior to return to service. The parts being modified would need to be assessed and new CAR submitted as part of the application for the new TC. Sit down with the cert authority and make a plan. They make the rules and you have to show compliance.

I'm in the US, "foreign" means "not in the US". However, if I was British, "foreign" means "not in England". "Foreign" doesn't really mean much...

Assuming you are in the US or a country with regs like the FAR's, this is no different than using type certified components on an aircraft with an experimental airworthiness certificate. In that case you are still required to keep up with AD's and SB's for those components. The minute you start modifying the airframe it is no longer compliant with the type certificate or former airworthiness certificate and you now have something that can only be flown under an experimental certificate of some kind. So for those TC'd components you intend to continue using on the aircraft after you finish modifications and get a new TC for the aircraft as a whole, you had better keep up with all the requirements, otherwise you'll have a steep climb catching up at the end of the game getting the airworthiness certificate when all is said and done. Whomever is the DAR is going to want to see all that before you are given a signoff.


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What aircraft might have white wing tip lights?
I live near O'Hare airport and see hundreds of planes every day.  This evening a plane flew past that did not have the standard red - green wing tip lights.  It was white only on both sides.  It caught my attention because of that, and because the plane was unusually quiet...not silent, but quieter than most everything accept the smallest private planes.  Any suggestions as to what I saw?

The wingtip lights you saw are combo red/white and green/white lights. You will see the color when viewed from ahead and white when viewed from behind.

You don't tell us if you're viewing this aircraft from the front (approaching you) or the back (moving away from you), so let's look at all the options:
Aircraft have three colors of steady-burning navigation/position lights: Red on the left (port) side, Green on the right (starboard) side, and White at the aftmost position (tail). This diagram shows the required lighting coverage (as implemented on a typical small aircraft):

(With the exception of a "mast light" these are identical to naval vessel position lights - the function of a mast light is performed by the landing light, though it's not used as a "position light" the way the others are.)
On some aircraft there will also be aft-facing white position lights on the wingtips, combined with the navigation and strobe lights:

The aft-facing position lights on the wingtip improve visibility at night, particularly flying over brightly lit urban areas (a problem sailing vessels don't have). They also give a visual reference to determine the size (wingspan) of the aircraft.
Finally (just to throw another wrench in the works) some aircraft are equipped with wingtip "recognition lights" (forward-facing white lights on the wingtip):

These are typically used on the ground or in approach to landing, but when illuminated the brighter recognition lights can make the forward position lights difficult to see, particularly from the ground where your eyes probably aren't adapted for darkness.

So putting it all together:
If you're viewing the aircraft from the rear (it's flying away from you) you will only see white lights (either one or three white lights) and the aircraft's strobes or other intermittent anti-collision lights. You will thus know the aircraft is traveling away from you.
If you're viewing the aircraft from the front (it's flying directly toward you) you will see a red and green light (possibly with white taxi/landing/recognition lights as well, but the red and green at the wingtips are what you're looking for to identify the aircraft's direction of travel).
Again if the aircraft has wingtip "recognition lights" you may have trouble picking out the navigation lights.
If you're viewing the aircraft from the side (it's flying perpendicular to you) you will see either the Red or Green light until it passes in front of you, at which point one (or more) of the white lights will come into view.

Actually they are identical to marine navigation lights, where the 110 degree visibility is specified as 22.5 degrees (i.e. 2 compass points) abaft the beam, or 112.5 degrees - http://wow.uscgaux.info/content.php?unit=070-17-06&category=navigation-lights

@AndrewMedico You're right: I misremembered. "Red and green being reversed" would mean seeing the red light to the left of the green light, rather than to the right.

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Is the actual VMC to IMC transition a challenge (for IFR rated pilot/craft etc) if, say, sudden or unexpected?
I assume that even on an IFR flight, being in even marginal VMC can be helpful, and that pilots consciously or subconsciously use cues such as the horizon to assist them in their flight even though they are principally flying by instruments.
I was wondering if that makes a sudden transition to IMC a psychological challenge, particularly if unexpected. That must be quite a "task switch", scabbling for information, switching focus, and so on?
It seems like that might be much more of a personal challenge than when flying deep in IMC for some time (to a trained and qualified pilot/aircraft) when a routine of going from instrument to instrument is established along route.
Is this a major challenge or a minor or even unnoticeable one in the grand scheme of things?

If you are an IFR pilot hand flying in VMC and suddenly your horizon reference disappears, or becomes untrustworthy (flying over sloping terrain in low visibility, or flying between cloud layers that are sloping), you do have to make a conscious mental transition from external scanning to internal scanning and it will increase the stress level slightly when you're new, but this declines as you get experienced doing it and it eventually becomes a non-event.
This is mainly because if you are flying IFR a lot, especially commercially, you will be doing this all the time on departures in instrument conditions, where you take-off visually, looking outside, and immediately enter cloud, often even before it's time to engage the autopilot (you wouldn't really want to to do a lot of IFR flying without one).  So effectively you have to make that VMC to IMC transition on every departure in IMC weather that you hand fly while entering cloud and you get used to the look-out-to-look-in transition pretty fast.
So I would say the answer is yes to a new pilot, but quickly becomes no, once experienced a bit.  That being said, "grey area" conditions, like I mentioned at the start, where you need to go on the gauges even though there is still a view outside, would be more of a challenge compared to just charging into cloud where the view goes from green to grey instantly and the distraction of a misleading outside view isn't there. That requires a bit more concentration and self discipline to ignore the view outside, and therefore a bit more experience to drop the stress level of the transition.  But still, after doing it a number of times, it should be no big deal.

For an inadvertent entry into IMC on a VFR flight by an instrument rated and current pilot flying an IFR certified aircraft, the initial transition into instrument flight would not be difficult - at least for a competent instrument pilot.  They would immediately and instinctively transition into attitude instrument flight and could quickly gain control of the aircraft and maintain controlled flight.
The problem could come immediately thereafter as they are now operating an aircraft on instruments on a flight planned to be conducted under visual flight rules.  These flights are far more liberal on route planning, terrain and obstacle clearance, traffic separation, etc. as they are totally dependent upon visual reference for these tasks.  Often VFR flights are simply conducted by pilotage with only a cursory review of NOTAMS prior to departure.  They’re flown along custom routes that may not make of use of any electronic navigation aids nor any consideration taken for signal coverage, reception altitudes, instrument procedures at the planned destination, etc.  These factors can link together to form a accident chain very quickly.  Fly into a valley with patchy clouds and there’s a GPS outage you didn’t note in the preflight, you’re screwed.
Likewise you are now flying blind, either in controlled or uncontrolled airspace with no means to see and avoid traffic nor do you have ATC radar services available to you.  I’ve have the uncomfortable experience of watching a 737 pass over me at night in the clouds in KSAN Class B - all I saw of him was two luminous beams that were his landing lights glide over me.  And that was on an IFR flight plan with ATC services.  I’d hate to think of what that would have been like without it.
If this happens and you wander into Class B airspace,  expect a 709 ride from the FAA.  If this happens and you wander into the side of a mountain, you can expect a coffin.

Your question is very, very complex. Well, not the question as such, but the things that have an effect to the situation you describe.
Anything that happens suddenly in an airplane has varying effects, depending on at least (but not limited to)

has the pilot received proper training for such situations
is the pilot proficient with regards to the situation (I don't mean in a regulatory sense)
what is the personality of the pilot like
what is the psychophysiological state of the pilot
in case of a multi-crew flight, how well is the crew coordinated

If any of the aforementioned is less than satisfactory, it is reasonable to assume something might hit the fan. And talking about reasonable, if something actually goes wrong, one way to describe the failure is to use the "Swiss Cheese Model", aka "the Reason Model" (not because it deals with reason or reasonable stuff, but because it was created by D. Orlandella and J. T. Reason).
Now, the IR rating itself, while of course is necessary for successfull flight in IMC, does not at all guarantee survival in poor visibility. More important is experience, and self discipline. You see, I'd say that marginal VFR is harder to fly than dead zero visibility IMC. In IMC there is usually very little to distract you, and since you have nothing to reference your situation with, you stick with the gauges the best you can. If there is some visibility, the risk is, that an inexperienced pilot, or one with poor airmanship discards the gauges and loses situational awareness.
Professional pilots that fly alot have probably the best abilities when it comes to situations like the one in question, if company culture is of the right sort (strictly safety oriented).
Flying by gauges is not that difficult if training and practise are in order. Perhaps the most difficult part is to recognize when to switch from visual to instruments. There absolutely should be no in-between!
To add up, I have to say that a pilot that finds oneself suddenly and unexpectedly in IMC is not a very good pilot. We all make mistakes, that's for sure, but if you are properly trained, have been practising rigorously, are physically and mentally fit and not the sort of person who either freezes or acts overly confident in surprizing situations, it would be weird if anything went horribly wrong.


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How can I build the 40 hours instrument time required for an instrument rating?
14 CFR 61.65(d)(2) says:

(2) Forty hours of actual or simulated instrument time in the areas of operation listed in paragraph (c) of this section, of which 15 hours must have been received from an authorized instructor who holds an instrument-airplane rating, and the instrument time includes:

So 15 hours must be with an instructor.  What about the other 25?  Can I fly in instrument meteorological conditions (IMC) "solo" (not the hood) like I did for my private pilot license (PPL) after an instructor sign off?  Or does this just mean that I need another instrument rated (IR) pilot with me, but it doesn't necessarily have to be a certified flight instructor (CFI)?  If that is the case, and I use the hood rather than actual IMC, does the other pilot need an IR or just a PPL?
Basically, how do you fulfill the other 25 hours?

Not that it will change the answers in this case. IFR flight plans require a pilot on board that is IFR rated and current. You should consider splitting the four questions here into a few others, though.

Welcome to Aviation.SE.

Two words: safety pilot.

The remainder of the 25 hours can be completed with a Safety Pilot, a CFI, or a CFII.
A safety pilot must be able to act as PIC of the aircraft you are flying. Also, if the safety pilot is acting/desinated as PIC, both you and the safety pilot can log PIC time for when you are flying under the hood. If you are acting as PIC, the safety pilot can log SIC time for being a required flight crew member (FAR61.51(f)).
You cannot file an IFR flight plan or fly in IMC unless a current Instrumented Rated pilot is on board and acts as PIC.

Regarding your last sentence, the instrument rated pilot must also be the PIC and not simply on board.

It's important to note that the safety pilot permits flight in VMC only while the instrument trainee is under the hood.

@egid Not if the safety pilot is the PIC and instrument rated/current.

I actually don't think that's true. Got a link?

Sorry - I should clarify. As soon as the flight enters IMC, the non-instrument-rated pilot cannot act as sole manipulator or log PIC/instrument flight time.

This question seems to suggest that the Safety Pilot does not need to be able to act as PIC.  Is that Question/Answer incorrect?

@egid I logged lots of hours as IMC before getting my instrument rating. All of them were with a CFII, but there is no reason that you couldn’t log time if the safety pilot is comfortable with you handling the controls.

@egid That is not correct. If the instrument rated and current safety pilot acts as PIC and files IFR, both pilot can enter IMC logging PIC time. The safety pilot logs PIC because he is acting as PIC and is a required flight crew member. The IR student logs PIC time for being sole manipulator of control. And yes, anyone can be the sole manipulator of control under part 91 regardless of rating.

@fjch1997 In IMC, the safety pilot is the only crewmember required by the regs. Under simulated instrument, a safety pilot can log PIC time under 61.51(e)(1)(iii), as regulation requires two crewmembers for simulated instrument flight. Regulation does not require two crewmembers for actual instrument flight, and so the safety pilot is out of luck for logging the time.

@Chris Yes, only the instrument-rated pilot is the required flight crewmember. But both pilots meet the requirement for logging PIC time.

@fjch1997 Under what regulation?

Here are the requirements for simulated instrument flight with a safety pilot, taken from 91.109. They only need a private certificate, along with the appropriate ratings in that category and class, but not instrument.
14 CFR 91.109:

c) No person may operate a civil aircraft in simulated instrument
flight unless—
(1) The other control seat is occupied by a safety pilot who possesses
at least a private pilot certificate with category and class ratings
appropriate to the aircraft being flown.
(2) The safety pilot has adequate vision forward and to each side of
the aircraft, or a competent observer in the aircraft adequately
supplements the vision of the safety pilot; and
(3) Except in the case of lighter-than-air aircraft, that aircraft is
equipped with fully functioning dual controls. However, simulated
instrument flight may be conducted in a single-engine airplane,
equipped with a single, functioning, throwover control wheel, in place
of fixed, dual controls of the elevator and ailerons, when—
(i) The safety pilot has determined that the flight can be conducted
safely; and
(ii) The person manipulating the controls has at least a private pilot
certificate with appropriate category and class ratings.

If you don't want to use an instructor - which is the best and safest way to get those 25 hours - there are only two other ways I can think of to get them: use a safety pilot; or use time logged under another instrument rating.
14 CFR 91.109 explains the safety pilot requirements:

(c) No person may operate a civil aircraft in simulated instrument
  flight unless—
(1) The other control seat is occupied by a safety pilot who possesses
  at least a private pilot certificate with category and class ratings
  appropriate to the aircraft being flown.
  [...]

Note that if you use a safety pilot you have to log his/her name per 61.51 and - contrary to somewhat popular belief - the safety pilot does require a current medical (at least according to AOPA's lawyers).
The second way would be if you already have or had an instrument rating, probably a foreign one. In that case, the time logged under your foreign privileges is acceptable to the FAA for ratings purposes (see this question).
Note that your instructor will not sign you off for solo instrument flight after 15 hours. There is no instrument rating equivalent of the private solo endorsement: you can only fly under IFR (or below VFR minimums) after you pass the IR checkride. Even if you use an instrument rated 'safety pilot' in IMC then he must be acting PIC because you have no instrument rating. If you try to get around those rules you'll either kill yourself or be operating illegally.

Can the safety pilot use BasicMed?


text:
How do droops help to avoid stalls?
Droops are deployed on the leading edge of a wing of an aircraft, and they work by changing the camber of the wing.
How do they help in delaying stall?

You mean leading-edge slats?

Slats are different that Droops

Droops are similar to slats. Their advantage is that it has lower drag for the same lift, the disadvantage is that it does not generate the same maximum lift (source Airliners.net). The replacement of slats by droops is for noise reduction (see chart 11). The penalty is the maximum lift.

They are called leading-edge droop flaps. I have just had to correct Wikipedia. Please could you update your question accordingly?

Similar to a leading edge flap, fixed in the extended position with no gaps: The nose is lowered, so at high angles of attack the flow still has its stagnation point at the round nose where on an un-drooped nose it would had slipped below the nose section.

This reduces the suction peak near the nose of the upper surface pressure distribution and consequently makes recompression towards the trailing edge much easier. This helps to delay flow separation and to achieve higher angles of attack and lift. If an aircraft had a roll instability at high angle of attack, adding a drooped nose on the outer wing will cure it of misbehaving.
The downside is that now at low angles of attack a suction peak will form on the bottom side and might cause local flow separation. This increases the viscous drag just when this drag component dominates overall drag. Consequently, aircraft which had been modified with a drooped nose do not reach their old top speed anymore.


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How to do blade element momentum theory analysis for different geometries of airfoil, e.g. NACA airfoils?
I want to analyse NACA airfoils using BEMT. I have only yet done it for basic symmetric airfoils. I would like to know what all assumptions remain same in NACA airfoil analysis and to what degree it is accurate. Like for starters, will accounting for Cl-alpha change and geometrical changes in angle of attack be enough to analyse NACA airfoils?

To clarify: I usually hear of BEMT to analyze rotors or propellers, given particular airfoil sections.  Are you trying to analyze a variety of NACA airfoils so that you have an expanded set of airfoil tables to reference in a BEMT analysis?

It is for analysing rotors. I cant think of any difference to BEMT analysis except for the airfoil table changes when NACA airfoils are considered. I feel like the accuracy is going to be way off if that's just it

Technically, symmetrical airfoils are just NACA00xx airfoils, and I think that frames the problem better. If you do not use the right airfoil data -- particularly when moving from symmetrical to asymmetrical airfoils -- you are going to see significant errors in the results for sections that are pre-stall. But that's it if you are doing a traditional BEMT analysis...the described change in airfoils won't effect compressibility effects since neither are supercritical airfoils, and that's the only other change that comes to mind outside of the airfoil tables.

The only difference would be the lift and drag coefficients used.  You'd need those to be specific to the airfoil(s) you choose.  Momentum theory is otherwise not sensitive to the airfoil shape.
Given the same lift and drag, momentum theory will give you the same induced velocity.


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What is the temperature of flap linkages during takeoff and landing in passenger and fighter aircraft?
During takeoff and landing, what is the temperature of flap linkages in passenger or fighter jet aircraft?

Unless a linkage was directly in an exhaust flow, it would be the same temperature as the ambient air, no?  How would it be anything different?

During takeoff flap opens to provide lift.so is there any possibility of temperature rise due to high pressure during flap fully extended position?

No you need to be well past 200 kt for any kind of significant compressibility temperature rise, and that's only around leading edges.

Pooja, You might like to give some idea of what prompted the question. In case your question arose while trying to understand some related phenomenon it would be nice if you added something about that. You may like to read up on the terms TAT (Total air Temperature), OAT on ground, and SAT inflight, here.

Thanx John.Will u please tell me the temperature rise around leading edges.

skipper44 ,actually i want to identify an aircraft component having relative motion ,whose temperature rise above 150 deg C and what is the material of that component.After identifying that component,can it be replaceable with aluminum composite.This is all about my area of concern.

@PoojaDwivedi You really need to edit your original question to include the extra information you've given within comments. Comments are ephemeral and subject to deletion and/or moving to chat. Please edit your question to provide ALL relevant information.

Components like linkages on a wing flap system can be considered to be the local ambient temperature, subject to some lag if the plane is moving between large temperature changes, because of the time for the components to soak.
So a plane descending from 40000 ft after a cruise at that altitude may have components cold-soaked to ambient, say -40C, and if the airplane descends to 3000 ft to start an approach, where the temperature is +10C, by the time the airplane is at 3000 ft the components can be expected to be a bit cooler than ambient because of the lag time for the components to fully absorb the heat of the warmer lower temperatures.  How much lag would depend on a lot of factors, like the amount of exposure to the freestream, and things like heat being drawn toward cold fuel just ahead of the component.
This was a significant problem in fact on the CRJ200 program, because the screw jack flap actuators were sensitive to extreme cold and like to jam, and a good cold soak at high altitude followed by a quick descent and extension at low altitude, where it was still really cold down low (winter), could leave them still cold enough to have the system fail while still at zero.  There was a big AD related to it.


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Do lights on aircraft flash in a specific pattern?
On a clear night, everyone can spot planes quite easily: they have flashing lights. I have noticed that the pattern seems different for different planes, and tried to find a meaning.
What I saw so far is that they seem to have three lights that flash, two at the wings, one at the tail. Those at the wings flash two times (approximately per second, in quick succession), and that one at the tail flashes only once, along with the first flash of the wing.
Now that explains two patterns I seem to see from further away: Two flashes and one flash. It is probably that I am just not seeing the wings flashing for those where I only see one.
So far so good, but then again sometimes I see planes with more flashing, and those are faster. I had difficulties to count them, but it's at least three, maybe four quick flashes.
Do these different patterns have any meaning? I tried to match up the planes with the flight radar information, but since it is quite crowded around here, I wasn't really able to identify them. But whenever I saw that quick flashing ones, there was a military plane around, is that just coincidence?

Nothing more than Airbus vs Boeing vs others.

Yes they have a meaning, it's "don't crash into me!"

One day we'll flash landing lights to send Moss codes through the air.

Because we all know, @kevin, that a flying plane gathers no moss.  ;)

Here is the pattern for A320 https://utcaerospacesystems.com/wp-content/uploads/2018/04/06_0010-LED-Anti-Collision-Lighting-System-A320.pdf

Civilian aircraft have flashing lights based on manufacturer design preference.  As others have stated, aircraft like Boeing and Airbus have different patterns.
However, military aircraft can often select the pattern they want to use.  This helps military pilots identify key tactical aircraft during night operations, such as the tanker flying around the carrier.  It is definitely not coincidental that you noticed military aircraft with a unique pattern, although I'm truly shocked at your attention to detail.

No, the pattern has no meaning, though the double-flash does identify the plane as an Airbus; other manufacturers use a single flash.

I believe the MD-11 does doubles, too. And maybe some of the smaller stuff (Embraer, Canadair, ATR and the likes) but I can't remember now, and also it's been a while since I've been close to anything with fixed wings - other than automobiles, that is.

Example of anticolision lights pattern on military helicopter..

Pilots can select the pattern they want to use according to tactical situation:

Red flashing lights top and bottom of the aircraft are turned on when pilots are clear to start engine. If you see those lights you know that there is an aircraft with running engines. So it could be moving towards to you, so be careful.
Tail light is for it to be seen from behind. The aircraft behind of you knows there is an aircraft in front of him.
Flashing light at wings means that this aircraft is airborned or about to be.
Pilots turns that lights on when they are on the runway. These lights are stays put during the entire flight until the aircraft off the runway after landing.

Do you have any sources for these? I just came upon this question and noticed that everyone else is pretty much saying that the lights are different across manufacturers.

"Flashing light at wings" are called strobes, and are a form of anti collision lights. It depends on aircraft model and SOP when they're turned on. Some aircraft have no "Red flashing lights" called a beacon -- also an anti collision light -- these aircraft generally turn on the strobes before engine start.

As answered by Orko, FAA requests in the AIM manual for pilots to only turn strobes on just prior to takoff (and turn off immediately after landing) so the eyes of landing aircraft are not distracted or confused with the other runway lights such as the REIL - runway end identifier lights. The other information provided by Orko is common knowledge for any pilot or mechanic that has ever pre-flighted an airplane.

In general, lights flash for the same reason that hazard lights on a car flash; because flashing lights are easier to see than solid lights. This applies to a lot of things in aviation. Building lights, tower lights, aircraft lights all flash because it is easier to see a strobe in low visibility than a steady light. White strobes are also brighter and red strobes are less reactive to the eye (which is why cockpits use red light). All of these combined help to make strobes easier to see and identify.
As to the pattern, as many have mentioned there is no specification on a specific pattern that aircraft manufacturers need to follow. For an aircraft like an airbus, wing tips may have a different blink pattern because the manufacturer wanted it that way. If I could take a guess, it would be so you can identify the orientation of the aircraft if you cannot still see the solid colored lights.

There's no specification for a pattern of flashing, and significant variations exist among different airlines and military. There is a uniform requirement for position lights (steady red and green on the left and right wingtips, white on the tail) and an anti-collision light system which is one or more flashing lights which can be anywhere on the aircraft. US requirements are in 14 CFR 25.1401, and say that the system must appear to flash between 40 and 100 times a minute. Areas where lights overlap can have as many as 180 flashes per minute.

I don't know about civilian aircraft, but it's true that military aircraft have specific patterns. Each aircraft role flashes differently. Ill use F-18s as an example because they are multirole. An F-18 tanker might flash *, where an F-18 strike fighter might flash like *-
Both same aircraft but different jobs, hence different patterns

Do you have anything you can point to that backs up this claim?


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How can you find the best altitude for range or speed?
How can you select best cruise altitude (altitude for best range velocity) and maximum speed altitude?
The specific case is a turboprop aircraft of gross weight 8000 lb.

Pretty sure we need a lot more information besides gross weight to find altitude for best range or max speed.

Generally, climbing as high as you can would be close to the optimum strategy. In the end, the altitude is given by the optimum lift coefficient in cruise, which can be approximated as $$c_L = \sqrt{\frac{1-n_v}{n_v+3}\cdot \pi \cdot AR \cdot \epsilon \cdot c_{D0}}$$
Now it will be important to get the thrust over speed dependency right, which is expressed with $n_v$. A turboprop should have $n_v \approx -0.7$. The rest is determined by the aerodynamics of your plane.
Nomenclature:
    $c_L \:\:\:$ lift coefficient
    $n_v \:\:\:$  thrust exponent, as in $T \sim v^{n_v} $
    $\pi \:\:\:\:\:$  3.14159$\dots$
    $AR \:\:$  aspect ratio of the wing
    $\epsilon \:\:\:\:\:$  the wing's Oswald factor
    $c_{D0} \:$  zero-lift drag coefficient
If you have the optimum $c_L$, you need to find the altitude where level flight at cruise power will require this lift coefficient. Depending on the range of your small aircraft, you might spend most of the flight in climb and descent.
Maximum speed altitude: Draw the envelope at max power, and look for the rightmost point which can be trimmed. The equation above uses the quadratic polar approximation which works well at high lift coefficients, but for maximum speed the details of friction and parasitic drag are important, and they cannot be captured with a simple formula.

Do you have any reference explaining how the equation is derived in more detail?

@Jan Hudec: Please read this post: http://aviation.stackexchange.com/questions/3612/how-does-wind-affect-the-airspeed-that-i-should-fly-for-maximum-range-in-an-airp/3623#3623  Bonus: It gives you a more general answer, including the effect of wind.


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Case Study: Did I need to declare an emergency?
I am a fairly newly minted private pilot licensee (PPL). I had just taken off from a small private, (but open to the public) airfield. We are under the shelf of Class B, but are G up to 700 and then E to the B above at 4000.
My instructor noticed our oil Pressure gauge was very close to the red line, and so of course we  headed back. I was about to make a call to inform CTAF we would be crossing midfield and joining the left down wind. Instructor takes control and makes a call asking if any others are in the pattern. Then declare that we will be entering a right down wind (we are a left hand field).
A voice pipes up: Are you declaring an emergency?. I reply no, this is an urgency. (By now the wisdom of my instructor's decision to not cross midfield was clear: It would take much less time to land; it kept us out over paddocks should the situation get worse; It would not take us over houses as the left down wind would.)
Said voice pipes up again: This is the airfield manager, you must declare an emergency if you are using a right hand pattern. My Instructor told me to ignore him and make another call to CTAF asking for any traffic to report position. There was no traffic. We landed without incident.
Who was correct? The manager or us- and does anyone have a FAR/REF to support the conclusion. The old adage Aviate, Navigate, Communicate seems to apply here - but what might the manager be basing his claim on and why?

Sounds like a good situation ASRS report

Thanks Tom. I Was wondering- googled the ASRS - but then chickened out- am a visitor here in the lone star state - worry about visas, blow back etc

@TomLongstaff From my understanding, preventing that is one of the benefits of filing an ASRS report.

The very reason the ASRS system exists is to encourage pilots to report things without worrying about the report itself getting you violated since NASA is not a regulatory body. They act as a repository for information. If a problem does arise with the FAA sometimes the ASRS can head it off. I'd say it's always a good idea to file one.

Also, send a note to the airport manager thanking him for making a potentially dangerous situation less safe by distracting you from your job of getting safely back on the ground.

I'm not sure if an airport manager has any authority to enforce such rules (they very possibly do), but he should know that even a possible emergency trumps a rule like "left pattern only", and forcing you to "declare" isn't making anyone on the field more safe.

@JanHudec ASRS is kept by NASA.

If someone asks, "Are you declaring an emergency?", it means you probably should.   There is no downside to declaring!

Before we delve into this one.  Let's be clear that it is much easier for us to sit at a computer with books in hand and review decisions made under urgent circumstances.
Technically, the airport manager was correct here because per 14 CFR §91.126(b)(1):

"Each pilot of an airplane must make all turns of that airplane to the
  left unless the airport displays approved light signals or visual
  markings indicating that turns should be made to the right..."

There do not appear to be any caveats to that rule.
To un-bind a flight from this rule, one would need to take advantage of §91.3(b)

"In an in-flight emergency requiring immediate action, the pilot in
  command may deviate from any rule of this part to the extent required
  to meet that emergency."

In my personal experience, I have seen plenty of pilots fly around the pattern in whichever manner is convenient to them; entering on right or left bases for final, approaching for VFR straight-in landings from 15 miles out, etc.  So far, I haven't seen any repercussions for these actions, which is probably why your instructor did not agree with the airport manager.
Another thing that shouldn't go without being said is that this situation was none of the airport manager's darn business.
By verbally acknowledging that there was not an emergency, your instructor placed a liability on himself.  §91.3(b) allows the pilot to deviate from a part 91 rule, but to my knowledge, there is no statute that actually requires recognition of an emergency to be verbally declared or announced under non-ATC-controlled VFR flight.
By leaving the question, "is there an emergency?", unanswered, there is a chance to retrospectively say, "yes, we had an emergency and that's why we deviated from the rule."  However, since he told the airport manager that it was only an urgency he kind of shot himself in the foot if someone were to decide to raise the right turn as a legal issue, but I would be very surprised if anyone does.
To summarize and give you a more direct answer.

You had a valid emergency
You had no responsibility to verbally declare it
You did deviate from a legal regulation to meet the needs of that emergency

Sounds to me like you've got a very competent instructor.
Edit: I came across this Letter of Interpretation, which is sort of related to your situation.

Thank you Ryan - and yes I have - I am lucky. Actually It was I that uttered the word urgency,  not my instructor. - In retrospect I think it would have been far better to simply ask again if there is any traffic in the pattern (as opposed to an arm chair) and ignored the airport manager entirely.

@Tom my mistake.  I don't see a need to edit that because it's simply a semantic difference and no one is trying to point fingers here, as I'm sure you're aware.

@Ryan.Thank you for the letter.Very interesting reading. My take is that we were within our rights to deviate as it was a safety of flight issue. As you mention above perhaps the only mistake was declaring an urgent situation, rather than remaining mum. And of course very aware no one is pointing fingers. This forum feels like a very erudite space- great resource for newbs like myself!

@Tom indeed, and now I have learned this new word erudite.

In this case you guys were correct. Technically speaking traffic patterns at un-towered fields are not like ATC vectors from a tower. You are free to enter the pattern as you like (provided its in a safe manner) and joining it from the 45 to the downwind is simply what the FAA recommends. For that matter you technically don't have to make any radio calls and an un-towered field (but that is another matter)
It's worth taking a look at AC90-66A for more info on this matter.

Use of standard traffic patterns for all ‘aircraft and CTAF procedures
  by radio-equipped aircraft are recommended at all airports without
  operating control towers. However, it is recognized that other traffic
  patterns may already be in common use at some airports or that special
  circumstances or conditions exist that may prevent use of the standard
  traffic pattern

One might go out on a limb and say that this is a "special circumstance" in which case you are in the clear.
Furthermore

e. The FAA encourages pilots to use the standard traffic pattern.
  However, for those pilots who choose to execute a straight-in
  approach, maneuvering for and execution of the approach should be
  completed so as not to disrupt the flow of arriving and departing
  traffic. Therefore, pilots operating in the traffic pattern should be
  alert at all times to aircraft executing straight-in approaches.

Technically you can fly straight in if you like as well.
The only scenario where you may be in the wrong is if there is a local noise abatement that restricts you to left traffic or a specific runway during certain hours. The fact remains that if that were the case you would be more than capable of explaining your actions.
Now to the crux of the question: Did you need to declare an emergency?
No, you did not need to, but you should have; generally when in doubt you should declare and deal with the paperwork later. Declaring an emergency allows you to precede over other aircraft (and the others should be smart and yield the way). In this case your oil pressure could have led to a serious issue. While you were flying fine at the time the ways this could have played out are endless.
In addition to this I was doing some thinking last night on Ryan's point about not having to actually say you are in an emergency and he is correct that there is no legal requirement to say so. I think that the reason for this is such a law would be in direct contradiction with FAR 91.205 which does not require a radio be on board for VFR flight. As such they can not actually mandate you call out an emergency lest they mandate that you carry a radio.

Thank you Dave. Fascinating reading.Very interesting for me Interesting to note the different, yet very well informed opinions. As we had just turned out we were almost on the right down wind when the oil pressure issue was noticed by my instructor. You are absolutely spot on - it was my fear of paperwork that led me to utter the response- "this is an urgent situation, not an emergency." in retrospect I should have ignored the manager and simply asked again for any traffic to advise- hind sight is 20 20- a good learning experience for me, another day in the saddle for my instructor!

You are absolutely spot on - it was my fear of paperwork that led me to utter the response- "this is an urgent situation, not an emergency." The managers rather officious tone was rather frightening and added to the stress - Making the prospect of paperwork all the more frightening at the time-   in retrospect I should have ignored the manager and simply asked again for any traffic to advise- hind sight is 20 20- a good learning experience for me, another day in the saddle for my instructor!

sorry for the repost- am new to this site and floundering a little

No problems, @TomLongstaff, and welcome! Just hover over the little "x" to the right of the "x hours ago" tag and delete the duplicate comment.

I would note that "free to enter the pattern as you like" doesn't mean "free to make turns opposite the pattern once you're in it." As Ryan's answer cites, this is explicitly forbidden by the CFR, so, technically speaking, the airport manager was right, though his interference wasn't particularly necessary.

We would need to know the airport in question (even though the OP states is a Left Traffic field it may have other things published), but if there was published right traffic information they can use right traffic (and must make turns as necessary). I dont think anywhere i my answer I state that you can fly as you like in the pattern simply that you can enter the pattern in various ways.

On a related note, think carefully about asking for traffic in the pattern to advise.  In an urgency situation I would probably do the same, but many pilots consider the call either superfluous or annoying; and you may set yourself up for a false sense of security when nobody replies but there is NORDO traffic around or somebody is intentionally not responding.


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How should I read these climb and descent profile notations?
I use a tool called SimBrief to build virtual flight plans for a desktop flight simulator. As I've been getting more familiar with procedures, I've also been exploring more advanced settings in the builder as well as some parts of the OFP output.
One thing that I can't figure out even after consulting the tool's docs is how ascent and descent profiles are represented: for example, for a 737-800 on a medium-haul route, one of the available ascent profiles will be 250/280/78, while one of the decent profiles is 78/280/280.
How should these be read?

My guess would be 250 to 10,000 ft; 280 from 10k to crossover altitude, then Mach .78 after. Crossover altitude for that scenario would be roughly FL 325. Mach.78 seems a little high for a climb Mach, but I don't fly the 737. Also, 280 in the descent profile below 10k doesn't work, so my guess may be far from right.

I agree with @JWalters, although I wouldn’t say .78 is at all fast for a modern airliner’s climb profile. That’s about what the 737 NG uses, with some adjustments for head/tail wind (typically maybe +/- 20 kts and .02M, ballpark). Agree that I’d expect the last # in the descent profile to be 250 kts, not 280.

@RalphJ That could well be; as I said, I don't fly the 737. The jets that I fly have a typical climb profile of 250 up to crossover then .62.

For the climb profile, the first two values are indicated airspeed -- below 10,000 and above 10,000 feet MSL, and the final value is a Mach fraction. So 250/280/78 would be a climb of 250 knots below 10,000', 280 knots above 10,000', and transition to a climb of Mach .78 somewhere in the high 20's or low 30's (i.e. at the point where 280 KIAS = M 0.78).
For the descent profile, it is the reverse, initial Mach number from Cruise altitude until reaching the transition to indicated airspeed, then the IAS above 10,000', then the IAS below 10,000'.
The 250/280/78 climb profile is very standard for the 737 NG and Max aircraft; most airlines fly them at something fairly close to those speeds, using a Cost Index which starts there and then the FMC applies an adjustment for headwind or tailwind.  In a stiff headwind, the climb speed will increase up to maybe about 310 KIAS (as a ballpark) and Mach .80; with a strong tailwind the speed will go down to maybe 270 and Mach .76 (again, ballpark - exact Cost Index being used affects these adjustments).
The typical descent profile looks similar, although at least in the US we'd never use 280 knots below 10,000' -- it would always be 250 below 10.  If the country you were flying in didn't regulate that, you might do 280 down to close to pattern altitude, but I don't know what countries would allow that, and what you'd gain in time saved (not much) you'd pay for in terms of risk if you hit a big enough bird on or near the windscreen.
But that's what those numbers are almost certainly referring to.